This invention relates to electrochemical measurement and detection. More specifically, it relates to the use of a solid electrolyte in detecting the presence of the element chlorine and measuring the quantity present.
The use of solid electrolyte sensors for detecting oxygen, particularly in automotive exhaust gases, is well known. The present invention utilizes similar basic principles for detecting chlorine. The Nernst equation describes the behavior of sensing devices using solid electrolytes. When two media with different partial pressures, P.sub.1 and P.sub.2, of a particular substance present in both media are separated by a solid electrolyte (ionic conductor) and conducting electrodes are attached to both sides of the ionic conductor, an EMF is generated which is related to the partial pressures as follows: ##EQU1## where R is the gas constant, T is the absolute temperature, F is the Faraday constant, and n is the number of electrons per molecule of product from the overall cell reaction. If the system described by the above equation behaves non-ideally, the partial pressures must be replaced by fugacities. Another factor which may need to be considered in regard to a particular system is the rate of dissociation to form the ions which pass through the solid electrolyte. This may be a limiting factor to the transfer of ions through the electrolyte. The rate of dissociation can be calculated by means of the equilibrium constant for the dissociation reaction.
There is a need for improved methods and apparatus to detect chlorine, particularly in the area of petroleum refining, where the amount of chlorine present may be critical. For background information relating to the present invention, reference may be made to the book Solid Electrolytes and Their Applications, edited by Subbarao, Plenum Press, 1980.